External communication sources, such as portable cellular phones, have become increasingly popular and are used in many automobiles. Unfortunately, in order to use the phone, a user must hold the phone headset to his or her ear, which detracts from the ability of the user to properly and safely operate the automobile.
To overcome this problem, devices that allow for hands-free operation of a cellular phone in an automobile have been developed and are shown, for example, in Takano, U.S. Pat. No. 4,845,738 and Ono, U.S. Pat. No. 4,905,270. These prior art devices comprise a handset, typically installed near the driver's seat and into which the cellular phone can be inserted. The devices transmit incoming signals by wires from the cellular phone to an external amplifier and speaker system, which also must be installed somewhere inside of the automobile, most likely on the floor, the dashboard or in the trunk. Further, a microphone must also be installed in the automobile to transmit outgoing voice signals to the phone.
While these devices allow for hands-free operation of a cellular phone in an automobile, they have several drawbacks. Installation of the amplifiers, speakers, microphone and handset can be costly and time-consuming and is often too complicated for the average user. Also, such devices may crowd the inside of the automobile and interfere with safe and efficient operation thereof. Further, once the devices are installed, they are fixed in the automobile and are not easily removed. Thus, the devices are not portable and cannot be easily moved from one automobile to another.
Thus, there remains a need for a portable interface that allows hands-free operation of a cellular phone in an automobile without the need for external wires and components that involve costly and/or difficult installation and crowd the inside of the automobile.